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Converting 29.97 to 59.94 for Compositing Reduces Image Quality?

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Jared Peace
Converting 29.97 to 59.94 for Compositing Reduces Image Quality?
on Nov 29, 2011 at 2:55:26 am

Hello.

Whenever I need to do any sort of compositing on 29.97 interlaced footage in After Effects, I interpret the footage, set Fields to Lower Field First, then drag and drop the clip into a new comp. Then I go into comp settings and change the frame rate to 59.94. This temporarily halves the resolution but it provides whole frames for any shots involving motion. Then I nest that comp in a new comp, set the frame rate to 29.97, and render out the finished clip interlaced, lower field first. Same as it came in.

I've been using this technique for years and I thought it was preserving image quality, but in fact, it appears that maybe it isn't. I was looking over two identical shots - same camera set-up, both requiring compositing, but one had motion and one didn't. In one, the compositing was done at 29.97 and rendered out the same, and in the other, the 59.94 technique was used, and I'm now noticing that in elements of the shot that should be identical - static elements that weren't affected by the composite and should look exactly the same - thin, high-contrast horizontal lines and diagonal aliasing on the 59.94 comp look noticeably worse. By itself you'd think the shot was just as good, but when I zoom in and A/B it, it's obviously not.

Any thoughts on this?

Another similar problem with compositing in 29.97 vs. 59.94 which this A/B comparison brought to my attention is what happens when we introduce new picture elements into a shot. For example, let's say I have a .tiff I want to composite into a shot. If I composite it in at 29.97, then the full resolution (or the highest possible resolution) of that .tiff is being used, but if I composite it in at 59.94, then nest that comp in a 29.97 comp, then the full resolution of that .tiff is ONLY being used at 59.94, whereas at 29.97 it's being halved. I understand this is a fairly subtle problem and obviously I went for years without it really noticeably affecting the quality of my work, but now that I'm aware of it, I'm kind of curious if there isn't a better way.

Thanks COW.

Jared
http://www.jaredpeace.com


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Walter Soyka
Re: Converting 29.97 to 59.94 for Compositing Reduces Image Quality?
on Nov 29, 2011 at 3:25:31 pm

[Jared Peace] "Whenever I need to do any sort of compositing on 29.97 interlaced footage in After Effects, I interpret the footage, set Fields to Lower Field First, then drag and drop the clip into a new comp. Then I go into comp settings and change the frame rate to 59.94. This temporarily halves the resolution but it provides whole frames for any shots involving motion. Then I nest that comp in a new comp, set the frame rate to 29.97, and render out the finished clip interlaced, lower field first. Same as it came in."

You don't need the 59.94 comp in the middle. Separating fields on your footage is all that's necessary to allow AE to correctly transform and apply effects to interlaced footage. You can do all your work in a 29.97 comp and render with fields.


[Jared Peace] "I was looking over two identical shots - same camera set-up, both requiring compositing, but one had motion and one didn't. In one, the compositing was done at 29.97 and rendered out the same, and in the other, the 59.94 technique was used, and I'm now noticing that in elements of the shot that should be identical - static elements that weren't affected by the composite and should look exactly the same - thin, high-contrast horizontal lines and diagonal aliasing on the 59.94 comp look noticeably worse."

In the interpret footage dialog, have you checked the Preserve Edges box? From Interlaced video and separating fields [link]:
Click Preserve Edges (Best Quality Only) to increase image quality in nonmoving areas when the image is rendered at Best quality.


Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
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Jared Peace
Re: Converting 29.97 to 59.94 for Compositing Reduces Image Quality?
on Nov 30, 2011 at 6:15:40 am

Thanks for the reply.

Generally you don't need the 59.94 step when you're just applying effects, but when you're compositing different elements into a shot with all sorts of precise keyframed masks moving in time around various foreground, middle ground, and background layers, then working on interlaced footage doesn't provide accurate results.

Jared
http://www.jaredpeace.com


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Chris Wright
Re: Converting 29.97 to 59.94 for Compositing Reduces Image Quality?
on Dec 2, 2011 at 11:14:33 am

i know that if you don't have every hidden sub comp switch at wire,quality,best set to best, it can reduce your final reinterlacing.




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